If you’re like most of us, you’re not even sure there’s a difference between the two terms. There is.
A summary is very short and just gives the main idea. It’s usually just one paragraph, like the first paragraph of a newspaper article. It tells you what the main point is, then the rest of the story goes on the flesh it out and and support the point made in the first paragraph. Same thing with a book.
A synopsis goes much further. It highlights all the plot points – and sub-plot points – and takes you through the entire story. It usually leaves out character development almost completely, as well as all the other things that make the story interesting. But it does include all the plot twists and surprises.
So, a summary gives you enough to whet your appetite so you will then go and read the book or article. A synopsis pretty much ruins it if you then go and read the book or article.